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Specifier's choice: Terminal 5, Heathrow Airport

Sutherland Lyall talks to Richard Rogers Partnership's Mike Davis, the man behind the masterplan for Heathrow's new T5 complex, and Dennis Austin, leader of the roof team

Early last month they jacked up the first three-bay, 2,200-tonne section of Heathrow's new Terminal 5 roof. There are 22 bays in all, and work has already started on assembling the next lot of bays at ground level. The giant 156m-span arches, the middle sections of which are bow-string trusses, have settled into place on their tree-like strut and cable supports waiting for the final skin, the standing-seam Kalzip roof, whose aluminium trays have already been formed on the ground. In 10-high stacks, this went aloft with the aluminium sticks for the Sch³co rooflights, whose glass will be craned in later.

Size matters Following the successful public inquiry, Richard Rogers Partnership partner Mike Davis took over the T5 project and set up a dozen architectural teams for such issues as fl oor planning, vertical circulation, internal environment, edges, and the like. The groups were fl uid and sometimes merged.

Davis set the vision for the whole 96ha complex, which includes the main 400mlong terminal building and a slightly shorter satellite building nearly half a kilometre away. He says: 'I remember the title of one of Peter Cook's lectures, 'The Problem of Greater Number'. That's exactly what we have here.'

This is a seriously big project, and yet T5 is a tiddler in comparison with the building Davis has been masterminding at Madrid Airport, and which has provided a useful parallel learning experience. There he is dealing with a million square metres and such interesting problems as growing a bamboo forest on the roof. He says: 'At Madrid we had to have a new quarry opened because, halfway through laying the floor with this delicious stone, we found we had used up all the material in the first quarry.

Terminal 5 is much more concentrated.

It's phenomenally packed - and into a very complex little site. I say 'little', but it's actually the same area as Hyde Park.' Peter Cook's argument about greater number was not just about statistics and measurements. It was that extraordinary size brings with it the need for a completely different mindset on how you go about design. Davis says: 'There are 45 different stakeholders, from BAA through customs, immigration, security to retailing and maintenance, almost all of whose needs have to be satisfied. And there are maybe 30 million passengers a year. As just one part of that, how do you organise circulation so that there is always a self-regulated balance of luggage trolleys at the entrance and the exit?

That alone is a complex task and it has major fi nancial consequences, because getting it wrong could mean having to hire hundreds of staff just to redistribute trolleys. So it seemed best to make a shell with a completely free space inside. There could then be quite separate discussions about what went inside it. In the end there are six levels: three for check-in with big lifts providing a twominute Tube/train station-to-check-in-desk with the departures levels below.'

Pink fur and the light-bulb store Specification as we customarily know it has no meaning at this scale. Davis says: 'There's no individual selection [on the basis of whim] by the architect but large-scale concurrent e ngineering. You can't just say you've decided to go with the pink fur. The quantities are colossal. You can't just go in and pick a nice carpet just like that because you will be buying a square mile of that nice carpet. And choosing a door handle: what you are actually choosing is 30,000 door handles. That's probably a year's production for any manufacturer. So then you get into a long debate about whether it's a standard item or a special.' And what are the implications in terms of whether you design it or not, and what does this mean for long-term maintenance?

Davis talks about the Heathrow lightbulb warehouse. He hasn't located it yet but, he says, it must contain millions of different light bulbs for all the thousands of different fittings that have been installed over the many years of the airport's life.

The metaphor of the Heathrow light-bulb warehouse lurks behind every thought about materials and product selection.

As with Just In Time, fi rst developed as a process at Toyota, concurrent engineering is a post-Taylorist management/operational approach for product development whose object is to improve the processes of design, production, operation and maintenance. Its primary platform is that useful results can be achieved if all the key people involved in the various sequential steps become even more involved in the earlier steps. So all the disciplines work together and share data throughout all phases of the product life cycle - hence the use of the term 'concurrent'.

Because construction is a process, concurrent engineering neatly translates across - especially to very large-scale projects. 'One consequence, ' Davis says, 'is that because you are working with the contractors you tend to have to design things to suit their capabilities. It's a group operation.'

The Rogers practice is committed to the idea. Dennis Austin is leader of the roof team. He says of concurrent engineering: 'I was completely won over by the process.

I'll have diffi culty getting back into the conventional sequence of pre-tender, tender and then holding our breath while we get in the tenders and playing volleyball with shop drawings. And the contractor taking the owner aside and saying?' Favourite things An important element in the T5 design process is that BAA, which has operated as a skilled professional building client for decades, has rationalised its construction supply chain. This involved setting up a list of preferred suppliers from architecture to manufacture, so that at the very beginning of the design programme major contractors such as Rowen Structures could be appointed to the design team.

BAA's preferred supplier programme meant that the main players, the lead professional consultants and the lead specialist contractors, known as the firsttier suppliers, were all known - all 16 of them. More recently, Hathaway, the lead roofi ng contractor, had been chosen from the approved BAA list on the basis, as Austin puts it, 'of our thoughts about their ability to perform on and off-site, what their drawing offi ce was like, and whether they had their own workshops or jobbed work out. It had nothing to do with price. It was everything to do with how they would fit in with the team.' The team comprises three architectural practices, including Rogers;

engineer Arup; two cost consultants, Turner & Townsend and EC Harris; services engineer DSSR; and Laing, which was there as the construction manager.

No tenders, no contract, open book The BAA contract is not actually a contract in the confrontational JCT sense but is formally known as a framework agreement.

Austin explains: 'It's an open letter, which says that the supplier will commit to supply at the least possible cost to BAA. There are incentives for speed and meeting deadlines and targets. Everything is open book and everybody at fi rst-tier level is paid for the work they do. It means there is quite a lot of bureaucracy and checking, but it meant that if the welding took 200 hours instead of 150, BAA paid, because that was how long it took.' BAA also had an open-book arrangement with second-tier contractors, but not particularly with the third-tier contractors. But in this process, prices are agreed - there is no pitching. Austin says: 'We did no tender drawings because nothing was tendered. It simply didn't work that way.' This is a different way of practising architecture. Austin says: 'Seven years ago someone had a great vision and got everyone at BAA saying: 'We want you all to work it out together.' Some people were very cynical, but for the last seven years most have been patient, enormously patient. We have sat and listened and had conversations about how the terminal could be fabricated and built and we have watched the scheme develop in our collective hands.

'Contractors normally draw in order to build. But for the last three years now we have had Hathaways drawing with us.

We were able to change the nature of the talent pool. They were able to think on their feet and sketch their ideas and that has really paid off. Rowen's procurement people were really great in getting us access to the foundry's technology. We really took concurrent engineering to a level where we drew less so that they could build more.

'We had a fantastic 3D modeller so that when we were dealing with the external form they were there with us, and the Arup engineers, who were making sure that the sections were beefy enough not to affect the structure. It was a way of drawing - and of handing information to the foundry.

Then the wood patterns were cut on CNC machines directly from our fi les, ready to make the castings.'

Robotic manoeuvres The design discussions over the roof, Austin says: 'had included a 3D waveform diagrid that involved a whole host of relatively small-cast nodes. The steel people, Rowen Structures, were against the scheme because the intricate geometry meant on-site welding and bolting. BAA was against the idea too.' There followed a series of design brainstorms until roughly the present scheme was arrived at. Austin says: 'Rowen liked the new geometry because there was a recognisable hierarchy of primary, secondary and tertiary members.' Now attached to the structural proposition, Rowen thought it would be an even better idea to bring in PPTH, a Finnish bridge builder with a specialism in robotic welding and good experience of making deep beams.

Austin says: 'We spoke with them and were excited at what they could do and we then worked with them on a trapezoidal section beam whose geometry was possible but whose costs weren't.' Eventually, by getting to understand the fabrication process, the design team was able to develop a section with overhanging lips that act as guideline rails for the robot welding machines working on the inverted beams. Austin says: 'The way it looks is directly based on the way we knew it was going to be made. We then used the same detail for all the spars.' He explains: 'What happened then was that Rowen decided it was more sensible to pass over the fabrication of the primary arches. They had robotic welding but not for curved structures. Doing it would stretch their existing capacity unreasonably. So they brought in structural steel specialist Watson (which they bought) and which worked with PPTH so that 90 per cent of the roof steel, primaries and secondaries, were made in Finland, shipped over and, using enormous shear connections, bolted together on site.'

Tolerating tolerances With such an enormous building, it seems overly pedantic to talk about sub-millimetre tolerances. Especially when, as Austin puts it, 'you can't really control molten steel when it's being poured out of a ladle at 1,600 °C.

Erectors, too, think in terms of doubledigit millimetres. But early on we would go to meetings and the machinists would talk about microns, which is what they were used to dealing with - even on castings the size of the giant shear connectors used on T5. The Arup people mediated between the two and said we need to talk single-digit millimetres.

'And then the erectors would say: 'It's fi ne for you because you are inserting that pin in a shop environment and you will use freon to freeze it a tad so that it fits. You can't do that in the field.' So Arup would say: 'OK we'll open up the diameter of the hole a bit.' Arup's Steve McKechnie, who had caught on to the vision, was fantastic.' With the geometry of the main roof structure established, the design team, including roofi g contractor Hathaway, devised prefabricated panels that could be dropped in on the secondary and tertiary structural members. Hathaway developed a 6 x 3m cassette with a C-section cold-rolled steel frame. On the bottom is a face made up of 35 per cent perforated aluminium planks, with steel decking planks on top sandwiching a thick acoustic blanket. On top of the decking is a sound-breaker board, then a series of Z channels to take top-hat clips for the Kalzip trays. So the procedure is that the installer lays in these cassettes with an attached vapour-control layer on top, which is lapped over the downhill panel, enabling the cassettes to be temporarily selfweathered. All the preparatory work is done in Bishop Auckland, where Hathaway put up a new building to assemble the cassettes.

Kalzip trays are used for the 101m-long middle section of the roof. They are fieldextruded while the structure is on the ground and have a free ride up when the roof is jacked. The clips have been designed to take the anticipated 280mm of movement due to wind uplift, and Corus has allowed for a greater degree of thermal expansion than usual. The trays will be fixed finally when the geometry of the newly jacked structure has settled down.

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